User needs

• For window washing companies, speed in terms of surface area cleaned per unit of time is of major importance. The higher the speed with which the windows can be cleaned, the more profit that can be made. The goal is to reach a speed of 71 m² / hr, which is the mean of the three considered window cleaning robots as can be seen in the table below. This seems an acceptable requirement for the model.
• Water consumption should be as low as possible, since this has an impact on the speed of the cleaning process (provided that the robot has an on-board water tank that needs to be refilled) and also has a minor impact on the total cost of the cleaning job. All current window cleaning robots of the here considered size do not have a water supply or tank, but use detergent instead. The innovate part of the model is therefore that a water supply is included. This is an improvement since this is better for the environment. The requirement for the water consumption is based on a bigger window cleaning robot (GEKKO Facade Robot [7]) which has a water consumption of approximately 1 L/min. Because this bigger robot has a size of around 4 times the size of the considered cleaning robots, a requirement of 0.25 L/min seems suitable.
• Energy consumption should be as low as possible, since this has an impact on the total cost of the cleaning job. The requirement for the energy consumption is also determined by averaging over the different window cleaning robots in the table above: 73.5 W.

Type	WINDORO [2,5]	WinBot 950 [2,3,4,6]	Hobot 268 [1,2]	Mean
Dimensions cleaning surface	21.8 x 21.1 cm	27.2 x 27.2 cm	24 x 24 cm	24.33 x 24.1 cm
Weight	2.9 kg	2.3 kg	1.2 kg	2.1 kg
Cleaning speed	62 m2	125 m2	25 m2	71 m2
Energy consumption	-	75 W	72 W	73.5 W